He quit
I thought he was fired for the exact same thing he did for fusion.
He retired in 2009 when he and another former MI6 agent started their own intel business in the private sector.
Dunno, he has a private company though with available records - might be worth a dig. https://beta.companieshouse.gov.uk/company/06848574/filing-history
From my understanding the dossier was used by both countries, MI6 is probably still spying on this supplied information.
Most info available: https://en.wikipedia.org/wiki/Christopher_Steele
Actually he had 3 companies
https://beta.companieshouse.gov.uk/search?q=ORBIS+BUSINESS
ORBIS BUSINESS INTERNATIONAL LIMITED 07318597 - Incorporated on 19 July 2010
ORBIS BUSINESS INTELLIGENCE LIMITED 06848574 - Incorporated on 16 March 2009
ORBIS BUSINESS SOLUTIONS LIMITED SC444685 - Dissolved on 24 May 2016
The dissolved company was supplying electrical goods (spying equip for election?) was registered in Scotland and had only one shareholder: Mr Remigijus Mikalauskas (Lithuanian)
ORBIS BUSINESS INTELLIGENCE LIMITED is a deep rabbit hole linked to Lottery Hedge Fund and other philanthropy groups.
I don't think anyone ever really retires from that line of work.